Normal cell proliferation is regulated by a balance between growth-promoting proto-oncotenes and growth-constraining tumor-suppressor genes. Tumorigenesis can be caused by genetic alterations to the genome that result in the mutation of those cellular elements that govern the interpretation of cellular signals, such as potentiation of proto-oncogene activity or inactivation of tumor suppression. It is believed that the interpretation of these signals ultimately influences the growth and differentiation of a cell, and that misinterpretation of these signals can result in neoplastic growth (neoplasia).
Genetic alteration of the proto-oncogene Ras is believed to contribute to approximately 30% of all human tumors (Wiessmuller, L. and Wittinghofer, F. (1994), Cellular Signaling 6(3):247-267; Barbacid, M. (1987) A Rev. Biochem. 56, 779-827). The role that Ras plays in the pathogenesis of human tumors is specific to the type of tumor. Activating mutations in Ras itself are found in most types of human malignancies, and are highly represented in pancreatic cancer (80%), sporadic colorectal carcinomas (40-50%), human lung adenocarcinomas (15-24%), thyroid tumors (50%) and myeloid leukemia (30%) (Millis, NE et al. (1995) Cancer Res. 55:1444; Chaubert, P. et al. (1994), Am. J. Path. 144:767; Bos, J. (1989) Cancer Res. 49:4682). Ras activation is also demonstrated by upstream mitogenic signaling elements, notably by tyrosine receptor kinases (RTKs). These upstream elements, if amplified or overexpressed, ultimately result in elevated Ras activity by the signal transduction activity of Ras. Examples of this include overexpression of PDGFR in certain forms of glioblastomas , as well as in c-erbB-2/neu in breast cancer (Levitzki, A. (1994) Eur. J. Biochem. 226:1; James, P. W., et al. (1994) Oncogene 9:3601; Bos, J. (1989) Cancer Res. 49:4682).
Current methods of treatment for neoplasia include surgery, chemotherapy and radiation. Surgery is typically used as the primary treatment for early stages of cancer; however, many tumors cannot be completely removed by surgical means. In addition, metastatic growth of neoplasms may prevent complete cure of cancer by surgery. Chemotherapy involves administration of compounds having antitumor activity, such as alkylating agents, antimetabolites, and antitumor antibiotics. The efficacy of chemotherapy is often limited by severe side effects, including nausea and vomiting, bone marrow depression, renal damage, and central nervous system depression. Radiation therapy relies on the greater ability of normal cells, in contrast with neoplastic cells, to repair themselves after treatment with radiation. Radiotherapy cannot be used to treat many neoplasms, however, because of the sensitivity of tissue surrounding the tumor. In addition, certain tumors have demonstrated resistance to radiotherapy and such may be dependent on oncogene or anti-oncogene status of the cell (Lee. J. M. et al. (1993) PNAS 90:5742-5746; Lowe. S. W. et al. (1994) Science, 266:807-810; Raybaud-Diogene. H. et al. (1997) J. Clin. Oncology, 15(3):1030-1038). In view of the drawbacks associated with the current means for treating neoplastic growth, the need still exists for improved methods for the treatment of most types of cancers.
The present invention pertains to methods for treating neoplasia in a mammal, using reovirus. Reovirus is administered to a neoplasm, in which an element of the Ras signaling pathway (either upstream or downstream) is activated to an extent that results in reovirus-mediated oncolysis of cells of the neoplasm. The reovirus can be administered in a single dose or in multiple doses; furthermore, more than one neoplasm in an individual mammal can be treated concurrently. Both solid neoplasms and hematopoietic neoplasms can be targeted. The reovirus is administered so that it contacts cells of the mammal (e.g., by injection directly into a solid neoplasm, or intravenously into the mammal for a hematopoietic neoplasm). The methods can be used to treat neoplasia in a variety of mammals, including mice, dogs, cats, sheep, goats, cows, horses, pigs, and non-human primates. Preferably, the methods are used to treat neoplasia in humans.
The methods of the invention provide an effective means to treat neoplasia, without the side effects associated with other forms of cancer therapy. Furthermore, because reovirus is not known to be associated with disease, any safety concerns associated with deliberate administration of a virus are minimized.